Association of luteal blood flow with follicular size, serum estrogen and progesterone concentrations, and the inducibility of luteolysis by PGF2α in dairy cows.

The aim of this study was to investigate the compatibility of the visual evaluation result of the blood flow characteristics and the blood flow measurements of the CL and the predictability of the responses given by corpora lutea with varying levels of blood flow to an induction of luteolysis by a PGF2α injection and to determine the possibility of increase in serum estrogen and progesterone concentrations in parallel with increased luteal blood flow (LBF). The cows, bearing a CL (n = 60; postpartum 35 days), were injected with PGF2α and were monitored for signs of estrous following the first injection. The cows, which did not show estrous signs, were examined for the presence of a CL on Day 14, whereas those that showed signs of estrous were examined on Day 10 following the onset of estrous. The level of LBF was visually graded as + (low; GI), ++ (medium; GII), +++ (high; GIII), and ++++ (very high; GIV). Immediately after the examination of LBFs, a second intramuscular injection of PGF2α was injected. In the cows, which were determined to be in estrous, the diameter of the Graafian follicles was measured by B-mode ultrasonography. Subsequently, these animals were artificially inseminated. The animals, which did not show estrous after the second injection, were examined as previously described and monitored for signs of estrous. A strong correlation (r = 0.654; P < 0.001) was determined to exist between the results of the visual examination of the images and the results obtained for the LBF area with the use of the Pixel Flux software. GIII (0.83 ± 0.15 cm2) and GIV (1.03 ± 0.48 cm2) were found to differ from GI (0.47 ± 0.23 cm2) and GII (0.51 ± 0.12 cm2) for the size of the LBF (P < 0.001). Serum progesterone levels in groups (GI, GII, GIII, and GIV) were determined to be 4.44 ± 2.42 ng/mL, 6.03 ± 2.37 ng/mL, 7.01 ± 2.94 ng/mL, and 7.17 ± 1.69 ng/mL, respectively. The comparative evaluation of the study groups showed that the groups did not statistically differ for the period between PGF2α injection and the onset of estrous, mean Graafian follicle size and estrogen levels. No direct correlation existed between these reproductive parameters and LBF.